There is known in the prior art a scientific instrument or portable object such as a diver's watch or an altimeter, which comprises a case carrying a pressure sensor. The sensor includes a membrane and a transmission device. The membrane is capable of being mechanically deformed under the effect of external pressure acting on the transmission device. This device thus transfers said movement of deformation (representative of pressure) for example to amplify the movement in order to display the pressure value detected by the sensor.
It is also known to use these capsules as an energy source for timepieces. These capsules contain a liquid such as ethyl chloride. The liquid reacts to temperature change and vaporises when the temperature rises and thus increases the pressure inside the capsule. The capsule cooperates with a winding spring retained by a shell connected to a chain by a pulley. The latter winds the barrel spring in a series of back and forth motions via a click system, ratchet and intermediate wheel.
When the temperature rises, the capsule winds the winding spring so that the chain relaxes and releases the pulley. When the temperature drops, the capsule contracts, allowing the winding spring to pull on the chain and wind the barrel.
Generally, these capsules are made by assembling two shells or membranes via the periphery or edges thereof so that there is a space between the two membranes. The membranes forming the capsule are made of crystalline material, such as, for example, an alloy comprising copper and beryllium (Cu—Be).
Each material is characterized by its Young's modulus E or modulus of elasticity (generally expressed in GPa), characterizing its resistance to deformation. Further, each material is also characterized by its limit of elasticity σe (generally expressed in GPa) which represents the stress beyond which the material deforms plastically. Thus, it is possible to compare materials of a given thickness, by establishing the ratio of the limit of elasticity to the Young's modulus σe/E for each material, as said ratio is representative of the elastic deformation of each material. Thus, the higher the ratio, the higher the elastic deformation of the material will be. However, the crystalline materials used in the prior art, for example, the alloy Cu-Be, which has a Young's modulus E equal to 130 GPa and a typical limit of elasticity σe value of 1 GPa, give a low σe/E ratio of around 0.007. The elastic deformation of these crystalline alloy capsules is consequently limited. In an application to an altimeter or energy source for winding a barrel, this respectively means a limited measuring range and a low winding force.
Further, since this elastic limit is low, when the capsule deforms, it comes close to its plastic deformation limit under low levels of stress with the risk of not being able to return to its initial shape. To prevent this type of deformation, limits are placed on the deformation of the capsule, i.e. the amplitude of movement of the capsule is deliberately limited. It is clear then that, for the altimeter application, the transfer movement must be amplified. This then causes a noise which is harmful to the altimeter and, incidentally, to the display of the measured value.
Moreover, the space between the membranes is placed under vacuum or filled with liquid. The capsule must then be sealed against leakage. To achieve this, a solder is generally used to secure the two membranes and seal said capsule against leakage.
This method of assembling and sealing the capsule limits the type of materials that can be used. Indeed, those skilled in the art may envisage using materials with better mechanical properties such as metallic glass or amorphous metals. However, the use of such materials with the generally used manufacturing method described above will be rejected. This choice is made because those skilled in the art will have the preconceived idea that the usual technique cannot be used to make a capsule without altering the characteristics of the capsule. Indeed, they will have the preconceived idea that using soldering to assemble and seal the capsule will alter the properties of the amorphous material of which it is formed, since the soldering operation requires an increase in temperature. This temperature increase may then cause the amorphous metal to crystallise if the temperature attains a temperature between the crystallisation temperature and the vitreous transition temperature of said amorphous metal.
This partial crystallisation of the capsule causes an alteration of its features and thus results in different behaviour. Those skilled in the art are not therefore attracted by the use of amorphous metals to manufacture a capsule.